A directional coupler has a through line through which a signal passes and at least one coupled line that samples the signal. At a basic level, a high-power directional coupler causes a sample of an electromagnetic wave propagating on the through line to propagate on the coupled line. Therefore, the coupled line serves to sample the signal on the through line. A directional coupler is capable of sampling signals propagating in two different directions. A signal flowing in a first direction on the through line is sampled on one port of the coupled line, while a signal flowing in the opposite direction is sampled on the other port of the coupled line.
To measure output power or other high-power signals in a system, high-power handling capability is desirable for dual directional couplers. For example, dual directional couplers with high-power handling capabilities are well-suited to measure the output power of a base station within a cellular network. High-power directional couplers are also well-suited to measure the return loss of base station antennas by measuring both the forward power, which propagates from the base station to the antenna, and also the reverse power, which is reflected from the antenna and propagates in the opposite direction.
Although such directional couplers, including dual directional couplers, are known, for example, from U.S. Pat. Nos. 6,066,994, 6,573,807 and 6,600,307, all known directional couplers suffer from a number of disadvantages, particularly in their design and their manufacturability.